Lighting control device

ABSTRACT

Photoelectric control device for switching loads such as street lighting luminaires on and off in response to ambient light levels. The circuit includes a photoelectric cell and a positive temperature co-efficient resistor (PTCR) connected in series across the luminaire load and normally closed contacts of a thermal switch in series with the luminaire load operating in response to the heat level of the PTCR, which thereby serves to compensate for varying levels of ambient temperature.

United States Patent Turner 1 1 LIGHTING CONTROL DEVICE [75] Inventor:Charlie B. Turner, l-lendersonville,

v NC.

[73] Assignee: General Electric Company [22] Filed: Nov. 23, 1971 211Appl. No.: 201,278

[52] US. Cl. ..250/206, 315/159, 337/378,

- 250/239 [51] Int. Cl ..HOlj 39/12 [58] Field of Search ..250/239, 206,214;

[56] References Cited UNITED STATES PATENTS 3,633,036 1/1972 Nuckolls..315/159 x 1 Apr. 10, 1973 3,538,379 11/1970 Berlin ..250/239 X3,056,035 9/ 1962 Bemheim ..250/239 3,496,422 2/1970 Horowitz ..250/239X Primary ExarriinerWalter Stolwein Attorney-Sidney Greenberg et a1.

[5 7] ABSTRACT Photoelectric control device for switching loads such asstreet lighting luminaires on and off in response to ambient lightlevels. The circuit includes a photoelectric cell and a positivetemperature co-efficient resistor (PTCR) connected in series across theluminaire load and normally closed contacts of a thermal switch I inseries with the luminaire load operating in response to the heat levelof the P'TCR, which thereby serves to compensate for varying levels ofambient temperature.

1 Claim, 2 Drawing Figures PATENTED APR 1 01973 a f, M H J no w rm nI... m $1 s Z j LIGHTING CONTROL DEVICE The present invention relates tocontrol devices for operating electrical systems such as street lightingequipment in response to ambient conditions.

It is an object of the invention to provide a control device of theabove type which is simple in construction, economical to manufacture,and reliable in operation.

It is a particular object of the invention to provide a lighting controldevice of the above type which includes a thermal switch for turning theluminaire load on and off and which compensates for variations inambient temperature and other conditions adversely affecting itsoperation, and which may be operated from power supply sources ofvarious voltage levels.

Other objects and advantages will become apparent from the followingdescription and the appended claims.

With the above objects in view, the present invention relates to acontrol device for controlling the operation of a load comprising, incombination, electric current supply means, photosensitive variableresistance means connected across the electric current supply means,temperature sensitive variable resistance means connected in series withthe photosensitive variable resistance means and operating in responseto variations in current therethrough and in ambient temperature forproducing varying levels of heat, and thermal switch means operating inresponse to the heat produced by the temperature sensitive variableresistance means for controlling the operation of the load. Inaccordance with a particular aspect of the invention, the temperaturesensitive variable resistance means has a positive temperatureco-efficient whereby its resistance increases with an increase intemperature and decreases with a decrease in temperature, so as to limitthe heat produced thereby and to accelerate its production of heat underlow ambient temperature conditions.

The invention will be better understood from the following descriptiontaken in conjunction with the accompanying drawing, in which:

FIG. 1 is a circuit diagram of an embodiment of the temperatureregulated control device of the invention; and

FIG. 2 is a sectional view of a thermal switch which may be employed inthe FIG. 1 device.

Referring now to the drawing, and particularly to FIG. 1, there is showna photoelectric control device connected to supply lines 1 and 2 havingterminals 3 for connection to a suitable power supply, which may beeither alternating or direct current. Load 4, which ina typicalapplication of the control device is a street lighting luminaire, isconnected to supply lines 1 and 2 for energization by the power supply.Connected to supply lines 1 and 2 across load 4 is photoelectric cell 5,such as a variable resistance cadmium sulfide cell of known type, whichis exposed to ambient light rays. Connected in series with photoelectriccell 5 as shown in a temperature sensitive variable resistance element 6which has a positive temperature co-efficient whereby it increases inresistance with an increase in temperature. As a result, the positivetemperature coefficient resistor (PTCR) 6 functions as a combinedheating resistance and as a protective self-temperature-limiting device.Such PTCRs are readily available commercially, and a particular typewhich has been found satisfactory is in the form of a disk composedmainly of barium titanate.

In the illustrated embodiment, PTCR 6 actuates the normally closedcontacts of a thermal switch 7 which is arranged in proximity to, i.e.,in thermal contact with, PTCR 6, and having its contacts connected tothe supply line in series with load 4, so as to control the operation ofthe load in response to the heat level of PTCR 6.

An embodiment of a thermal switch in operative association with a PTCRwhich may be used in practicing the invention is shown in FIG. 2. Asthere illustrated, the switch comprises a housing 8 of electricallyinsulating material enclosing normally closed contacts 9, 10 connectedby leads 9a, 10a respectively to the load and the supply line. Thecontacts are adapted to be opened by means of a rod 11 arranged with itsbottom end engaging contact 9 and its top end engaging bi-metallic disk12, which, as will be understood, flexes when heated to push rod 11downwardly to open contacts 9, 10. Arranged immediately abovebi-metallic disk 12 is PTCR 6 which is held in'place in housing 8 byspring 13 and having lead connectors 14, 15 connected to opposite sidesthereof. Connector 15 is connected by lead 16 to lead as shown.

Spark gap 19 connected in shunt with PTCR 6 and photoelectric cell 5serves to protect these components from high voltage surges, andresistor 18 in series therewith serves to limit or suppress the surgewhen spark gap 19 conducts during high voltage conditions.

In the operation of the disclosed control device, current flows throughPTCR 6 when ambient light striking photoelectric cell 5 decreases theresistance of the latter. The contacts of thermal switch 7 are normallyclosed during the hours of darkness, since during this period theresistance of photoelectric cell 5 is high and little or no currentpasses through PTCR 6. As the intensity of the light rays increases atdawn, the incidence of such light on photoelectic cell 5 decreases itsresistance, with the result that current passes therethrough to PTCR 6.If the thermal switch 7 is at moderate ambient temperature, e.g, 25C,the resistance of PTCR 6 is relatively low, and the passage of currenttherethrough will rapidly start heating the PTCR. The lower the ambienttemperature, the more rapid is the heating of the PTCR. When thermalswitch 7 reaches a temperature of, say, 100C, the switch ac tivates andopens its contacts 9, 10 and turns off luminaire load 4.

With increased heating, PTCR 6 increases its resistance and therebylimits the current passing therethrough, thus limiting the operatingtemperature of the thermal switch and associated parts. In a typicalcase, a thermal equilibrium would be reached at a temperature of, say,C, which is above the actuating temperature of thermal switch 6. PTCR 6in association with thermal switch 7 thus provides a self-correctingconstant temperature system which compensates for opposite extremes inambient temperature conditions and variations in line voltage. Forexample, when the circuit is in a hot luminaire, the heating wattscontributed by the PTCR are automatically reduced; and, conversely, ifthe luminaire is subjected to very cold ambient temperature, the heatingwatts generated by the PTCR are automatically increased and due to itscharacteristics, results in rapid turn-on of thermal switch 7 even undersevere cold conditions.

At dusk, the reverse process takes place, wherein the resistance ofphotoelectric cell increases until no actuating current flows to PTCR 6,and thermal switch 7 thencools off sufficiently to permit its contactsto close, thereby switching luminaire load 4 on. Once thermal switch 7has closed or opened, its thermal lag or differential is adequate tohold it in that position until a substantial variationin temperatureoccurs to change its position.

A further advantage afforded by the described system is that the circuitmay be operated from supply sources of different voltages, since underhigher voltages which might otherwise create excessive temperatures inthe circuit components the PTCR,.by increasing its resistance, tends toreduce the current and thereby the heat generated in the thermal'system.Thus, the described circuit may find application in a dual voltagesystem of 120 and 240 volts or in a varying voltage system.

While aparticular type of thermal switch has been shown and described,various other types of known or suitable thermal switchesmay be used.

While the positive temperature co-efticient element has been describedherein as a resistor, itwill be understood that other forms of devicesincluding semiconductors may provide equivalent function, i.e., generateheat by the passage of current and have a positive temperatureco-efficient in respect to such characteristic, and accordingly 7 allsuch devices are contemplated for use in accordance with the invention.

By virtue of the arrangement of the photoelectric cell 5 in series withPTCR 6 as shown, a number of advantages are obtained. For one thing, thephotoelectric cell operates somewhat as a switching means for operatingthe PTCR without the need for additional switch devices and accessoriestherefor, such as described in co-pending application Ser. No. 725,572ofJ.A. Nuckolls, filed Apr. 16, 1968 now US. Pat. No. 3,633,036, datedJan. 4, 1972, and assigned to the same assignee as the presentinvention. Thus, the use of the photoelectric cell as a switching meansas well as the light sensitive element in the described circuit providesthe necessary circuit functions with a minimum of components and cost.

The PTCR as represented here would typically have a 25C resistance valueof, say, 8,000 ohms and would not be below a minimum value of 3,500 ohmsdue to its operational characteristics. The circuit is therefore veryefficient in terms of power consumption from its input means. Anotherbenefit of the high resistance of the PTCR is that the selection of thevalue of the surge limiting resistor 18 is not as critical when comparedto the value of the PTCR when considering the voltage drops across thecircuit components while the PTCR is at its lowest resistance. This willminimize any deterioration of component parameter stability and thermalstress of the components and ohmic contacts.

While the present invention has been described with reference toparticular embodiments thereof, it will be understood that numerousmodifications may be made by those skilled in the art without actuallydeparting from the scope of the invention. Therefore, the appendedclaims are intended to cover all such equivalent variations as comewithin the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

l. A control device for controlling the operation of a load comprising,in combination, electric current supply means, photosensitive variableresistance means connected across said electric current supply means,temperature sensitive variable resistance means connected in series withsaid photosensitive variable re-- sistance means and operating inresponse to variations of current therethrough and in ambienttemperature for producing varying levels of heat, and thermal switchmeans operating in response to the heat produced by said temperaturesensitive variable resistance means for controlling the operation of theload, said temperature sensitive variable resistance means having apositive temperature co-efficient whereby its resistance increases withan increase in temperature and decreases with a decrease in temperature,so as to limit the heat produced thereby and to accelerate itsproduction of heat under low ambient temperature conditions, saidtemperature sensitive variable resistance means being in thermal contactwith said thermal switch means, and means for connecting said thermalswitch means in series with the load and said electric current supplymeans, said thermal switch means comprising a pair of contacts which arenormally closed when said temperature sensitive variable resistancemeans is in non-operative cool condition, and which are normally openwhen said temperature sensitive variable resistance means is inoperative, heat-generating condition, surge suppressing resistor meansconnected in series with said photosensitive means and said temperaturesensitive variable resistance means, and surge protective meansconnectedacross said photosensitive means and said temperature sensitive variableresistancemeans and in series with said surge suppressing resistormeans.

1. A control device for controlling the operation of a load comprising,in combination, electric current supply means, photosensitive variableresistance means connected across said electric current supply means,temperature sensitive variable resistance means connected in series withsaid photosensitive variable resistance means and operating in responseto variations of current therethrough and in ambient temperature forproducing varying levels of heat, and thermal switch means operating inresponse to the heat produced by said temperature sensitive variableresistance means for controlling the operation of the load, saidtemperature sensitive variable resistance means havinG a positivetemperature co-efficient whereby its resistance increases with anincrease in temperature and decreases with a decrease in temperature, soas to limit the heat produced thereby and to accelerate its productionof heat under low ambient temperature conditions, said temperaturesensitive variable resistance means being in thermal contact with saidthermal switch means, and means for connecting said thermal switch meansin series with the load and said electric current supply means, saidthermal switch means comprising a pair of contacts which are normallyclosed when said temperature sensitive variable resistance means is innon-operative cool condition, and which are normally open when saidtemperature sensitive variable resistance means is in operative,heat-generating condition, surge suppressing resistor means connected inseries with said photosensitive means and said temperature sensitivevariable resistance means, and surge protective means connected acrosssaid photosensitive means and said temperature sensitive variableresistance means and in series with said surge suppressing resistormeans.